The issue of replacement estrogen for post-menopausal women has created a variety of controversies in terms of potential benefits and potential risks. This project is concerned primarily with the prevention of estrogen-dependent neoplasia (breast or endometrium). In view of the extensive literature on both the potentially beneficial effects of estrogen treatment and the potentially detrimental effects, there is likely to be disagreement in the professional community and confusion and concern among the patient population and the public. The plan for the project is to enlist the cooperation of a selected group of physicians to participate in the demonstration by: (a) following recommended policies for surveillance, diagnosis and treatment, and follow-up for patients for whom they are prescribing estrogenic hormone therapy; and (b) providing data, or access to data collections, regarding therapeutic regimes for their patients on hormones and special information on those patients showing symptoms or signs such as bleeding or mammary masses. Recommended policies for surveillance, diagnosis and treatment and follow-up of patients will be developed by a Medical Steering Committee sponsored jointly by the Denver Medical Society, the Colorado Division of the American Cancer Society and the CRCC. Participating physicians will be provided consultation on surveillance, diagnosis and treatment of both endometrial and breast cancer as well as consultation for patient education. A supporting and reinforcing community education program will be directed at women over forty-five.